An image sensor, which is a device for detecting external optical image signals and converting the signals into electrical signals, has been mounted and widely used in various types of electronic equipment, and has been chiefly used especially in imaging devices.
In an image sensor, pixels that are photodetection units are arranged in a matrix form along row lines and column lines. In each pixel, a photoelectric conversion element is implemented and configured to convert light irradiated by a light irradiation device into an electrical signal.
Generally, the light irradiation device communicates with an image sensor so as to transmit a synchronizing signal indicating the irradiation of light to the image sensor. When a synchronizing signal is generated and transmitted, the image sensor may change its state from a standby mode to an image acquisition mode, read the electrical signal generated by light irradiation, and then acquire an image.
However, depending on the usage environment or the like of an imaging device, there are the cases where an image sensor and a light irradiation device are placed in a communication-disconnected state. In this case, an auto-trigger scheme is used in which an image sensor autonomously checks whether light has been irradiated and automatically triggers the driving of the image sensor.
However, in conventional technology, an additional photodetection element for determining whether light has been irradiated and generating a trigger signal is installed and used in the image sensor. Accordingly, there is inconvenience in that manufacturing cost is increased and the design of the image sensor is complicated.
Further, a conventional photodetection device is limited in promptly and accurately detecting whether light has been irradiated.